«Graphitische Einheit» (der Camosci-Decke)
Retour à «Kalkige Einheit» (der Camosci-Decke)Représentation et statut
- Couleur RGB
- R: 210 G: 170 B: 190
- Rang
- Formation lithostratigraphique
- Usage
- Ce terme est en usage.
- Status
- terme informel
Nomenclature
- Deutsch
- «Graphitische Einheit» (der Camosci-Decke)
- Français
- «Unité graphitique» (de la nappe des Camosci)
- Italiano
- «Unità grafitica» (della falda dei Camosci)
- English
- «Graphitic unit» (of the Camosci nappe)
- Variantes historiques
-
black phyllitic schists + calcschists complex (Bianchi et al. 1998), Graphitic unit = Toarcian-Aalenian (Carrupt 2003)
Description
- Épaisseur
- Environ 75 m (Carrupt 2003 Fig.2.4)
Hiérarchie et succession
- Unités hiérarchiquement subordonnées
Âge
- Âge au sommet
-
- Aalénien
- Âge à la base
-
- Toarcien
- Méthode de datation
-
Ennoyement de la plateforme / black shales au Toarcien-Aalénien (Carrupt 2003).
Références
- Définition
-
(2003) :
New stratigraphic, structural and geochemical data from the Val Formazza - Binntal area (Central Alps). Mémoires de Géologie (Lausanne) 41, 103 p.
p.17: Graphitic unit: is characterized by important lateral variations of facies (Fig.10.2).
The clearest succession is found in the western part of the nappe. A black graphitic micaschists (metashale, see microscopic description in paragraph III.4) containing porphyroblasts of garnets, immediately follows the Calcareous unit; the contact is clear-cut. It may contain rare thin levels of a calcareous graphitic micaschist (metamarls). Bianchi et al. (1998) found various heavily recristallized bioclasts in the black micaschist.
The eastern part is more complex. A calcareous graphitic micaschist (metamarls, see microscopic description in paragraph III.4) containing porphyroblasts of plagioclase or epidote overlies the Calcareous unit. The contact is gradual: thin levels (3 cm) of calcareous micaschist alternate with the calcitic marble; the latter becomes thinner upsection, whereas the calcareous micaschist thickens. Some graded bedding can be observed, indicating the local polarity (Fig.2.4). Up sequence, thin levels of black micaschist are interbedded within the calcareous micaschist.
The lateral transition between the western and the eastern part of the Graphitic unit is made over less than 2 m. A very hard and dark 50 cm-thick rock composed of graphite (50%), carbonate (29%), muscovite (12%), opaque (8%) and some accessory minerals, represents the transitional stage between the calcareous micaschist and the black micaschist.